Ball mill liner having bricks with wear indicators

ABSTRACT

A ball mill has a lining of bricks, selected ones of which have colored inserts extending toward the faces of the brick from the backs thereof for a distance of one-eighth to one-third the thicknesses of the bricks. When the bricks wear to the point of possibly failing, the colored inserts are readily visible to show that the liner requires replacement. Preferably the colored inserts are of the same refractory material as the bricks themselves and have a coloring material added thereto. This minimizes contamination of the material being ball milled.

United States Patent Robert F. Rea

Bloomfield Township, Mich. 797,604

Feb. 7, 1969 Feb. 23, 1971 Champion Spark Plug Company Toledo, OhioInventor Appl. No. Filed Patented Assignee BALL MILL LINER HAVING BRICKSWITH WEAR INDICATORS 7 Claims, 5 Drawing Figs.

US. Cl 241/182; 52/596; 264/60 Int. Cl B02c 17/22 Field of Search241/182,

183, 299, 300; 51/164; 52/105, 596; 264/29, 30, 60, (lnquired classes)220, 106, 110, 259

[56] References Cited UNITED STATES PATENTS 1,775,396 9/1930 Jackman52/596 2,184,601 12/1939 Konopicky 52/612 3,037,468 6/1962 Snellman52/105X 3,110,448 11/1963 Landes 241/182 Primary Examiner-Donald G.Kelly Att0rney0wen & Owen ABSTRACT: A ball mill has a lining of bricks,selected ones of which have colored inserts extending toward the facesof the brick from the backs thereof for a distance of one-eighth toone-third the thicknesses of the bricks. When the bricks wear to thepoint of possibly failing, the colored inserts are readily visible toshow that the liner requires replacement. Preferably the colored insertsare of the same refractory material as the bricks themselves and have acoloring material added thereto. This minimizes contamination of thematerial being ball milled.

BALL MILL LINER HAVING BRICKS WITH WEAR INDICATORS This application is adivision of my copending application, Ser. No. 533,033 filed Mar. 9,1966.

This invention relates to a ball mill with a liner of bricks, selectedones of which have means to indicate when a predetermined amount of wearof the brick has occurred.

A brick according to the invention is particularly useful in the linerof a ball mill container wherein the liner is subjected to wear whilethe ball mill is operated. In a ball mill, the rate of wear of the lineris difficult to determine and can vary greatly according to such factorsas the type and amount of the charge and the percent of solids therein,the size, density, hardness, and quantity of mill balls, and the rate ofrevolution of the ball mill container. It is also difficult to determinethe amount of wear, as by measuring the interior of the ball millcontainer, because the wear varies considerably for different portionsof the container. Such measurements are also difficult to obtain becausemore than half of the volume of the mill container is normally filledwith mill balls. An accurate measurement, consequently, is only possibleby removing many of the mill balls. This requires considerable labor andtime, particularly in larger mills which may contain several tons of themill balls. Consequently, it is easy for the liner to wear, before beingnoticed, to the extent that portions break away and contaminate thecharge. The wear also may be enough that the outer wall of the containeris exposed and worn by the mill balls to the point of contaminating thecharge or even causing .taLitset ila tslst tye The present inventionrelates to a ball mill liner having marking bricks with indicators .orinserts which, when exposed, indicate to the operator that the liner hasworn a predetermined amount. The marking bricks with the wear indicatorsneed not be placed throughout the liner but only in strategic locationswhere wear is greater, or in a predetermined pattern in the liner toprovide a representation of the wear. Either arrangement keeps the costof the liner at a minimum because the marking bricks, which are moreexpensive, are used only to the extent necessary. Also, the marked orcolored insert of each brick is only a small percentage of the overallbrick. This is important where high purity of the charge is requiredsince the contamination from the colored In a preferred form, thecolored insert of the marking brick is of a colored ceramic material,the ceramic material being the same as that used in the brick, so that aminimum difference in expansion or shrinkage will occur between thebrick and the insert and also so that the colored material will minimizecontamination of the charge, being of the same basic material as thebrick. V

i It is, therefore, principal object of the invention to provide a linerfor a ball mill which indicates when'a predetermined amount of wear hasoccurred.

7 Another object of the invention is to provide a ball mill liner havingmarking bricks with wear indicators, I IVIariy other objects andadvantages of the invention will be apparent from the following detaileddescription of preferred embodiments thereof, reference being made tothe accompanying drawing, in which:

FIG. 1 is a view in perspective, with parts broken away and with partsin section, of a ball mill having a liner embodying the invention;

FIG. 2 is a fragmentary view in perspective of a container of the ballmill of FIG. 1;

FIG. 3 is a view in perspective of a brick for the liner of the ballmill, which brick has a colored section therein;

FIG. 4 is a view in perspective, with parts broken away and with partsin section, of a slightly modified mill liner brick embodying theinvention; and

FIG. 5 is a view in perspective of a modified brick for the liner of theball mill, which brick has another type of colored section therein.

A ball mill ofthe general type for which the brick according to theinvention is particularly useful is shown in FIG. 1. The ball millbasically includes a drive unit 10 for rotating a ball mill container 12which is rotatably mounted on bearing units 14 and 16. The container 12has an outer metal wall 18 and a liner 20 and circular end walls 22which also can include outer metal walls and an inner ceramic linersimilar to the liner 20.

A particularly useful application for the ball millis in the mixing andgrinding of ceramic batch material for spark plug insulators. Suchinsulators require a high degree of purity as well as a high degree ofuniformity. Consequently, the materials must be mixed for long periodsof time and must be subjected to minimum contamination from the ceramicliner 20. In the event that the liner 20 becomes too thin during use,portions thereof can break away and contaminate the ceramic batchmaterial so as to impair the quality of the final spark plug or otherproduct made with the ceramic material. The wear also can be excessiveto the point that the outer metal wall 18 is exposed with small piecesof metal being worn away and contaminating the batch. Over a period oftime this wear even can cause failure of the outer wall 18 and result inexpensive repairs for the ball mill. The extent of the wear of the liner20 cannot be accurately determined by the length of time the ball millis in use because the wear varies greatly. As pointed out previously,the degree of wear will depend on the type and amount of the charge andpercent of solids, as well as the size, density, hardness, and quantityof the mill balls employed. The rate of revolution of the ball millcontainer 12 also is a factor in the rate of wear. Attempts have beenmade heretofore to determine the amount of wear of the liner by takingdiametrical measurements in the container 12. This has not been reliableor practical, however, because the wear in the container is not at alluniform and because the measurements are difficult and time consuming toobtain, due to the presence of the mill balls,

To overcome the above problems, marking bricks 24 are used as part ofthe liner 20. In one form of the invention, the brick 24, as shown inFIG. 3, is of generally rectangular configuration with slightly taperedsides to fit properly in the and mixed. The height of the section willbe from one-eighth to one-third the height of the brick 24 and usuallywill be from about one inch to about three inches thick. The width andlength of the colored section 28 are not critical but these dimensionsshould be small to minimize contamination, and yet be clearly visiblewhen exposed. If desired, however, the colored section can constitute alayer extending over the entire back of the brick.

The colored section 28 is preferably made of the same material as thebrick but with a colorant, preferably a strong one, added. By way ofexample, cobalt oxide or chromium oxide are desirable for alumina brick.However, small amounts of oxides of manganese, iron, or nickel, or anycombination, can also be used. Other colorants also can be used but areusually more costly than those just set forth. Examples are titanium,vanadium, and copper compounds. The colored sections can also be made byadding carbon or metals to the ceramic and firing in an inertatmosphere. Amounts of about one-half percent to about 2 percent, byweight, of the colorants added to the ceramic material are usuallysufficient. By making the section 28 of the same material as the brick,the effect of contamination is minimized since the contaminating coloredmaterial is the same as that of the brick except for the additionalcolorant,

By way of example, the brick and the insert can have the followingcompositions:

Moisture in the amount of 9-12 percent by weight can be added to thebatches and the final shaped brick and insert then fired to cone 16, forexample, for vitrification.

The brick 24 of FIG. 3 can be extruded in a continuous body and then cuttransversely to the predetermined brick length. The colored section 28also can be extruded separately and then cut transversely into sectionsequal substantially to the width of the slot 26. The slots 26 are thencut in the larger surface of the brick 24 and the colored sectionscemented in by means of a thick slip made from crushed, raw brick. Theextrusion pressures and other conditions for the brick 24 and thecolored section 28 should be alike and the orientation of the brick 24and the section 28 should be the same to prevent shrinkage cracks whichotherwise can occur, particularly since extruded pieces tend to have ahigh degree of shrinkage. Consequently, if the brick 24 is extrudedlengthwise, then the colored sections 28 should be extruded in widthsequal to the widths of the brick 24 or the length of the slot 26. Theextruded colored section is then cut transversely into sections equal tothe widths of the slots 26.

The bricks 24 need not be used throughout the liner but can be employedonly at strategic positions or in a predetermined pattern as shown inFIG. 2. In this manner, a minimum number of the more expensive markingbrick 24 need be employed and contamination by the exposed coloringsection is a minimum. By way of example, it is sufficient to have lessthan one out of ten ofthe bricks in the liner be a marking brick. Themill lining wear is usually considered to be about one percent of thecharge being milled. Further, if the marking section 28 includes 2percent of the colorant and occupies ten percent of the area of thebrick, the resulting contamination, even if all of the colored section28 were exposed, would only be 0.0002 percent. As a practical matter,the liner would be replaced when only a relatively few of all of thecolored marking sections 28 were exposed.

Another suitable marking brick 30 is shown in FIG. 4. This brick has acylindrical recess 32 in which a cylindrical marking section or insert34 is located. The section 34 can be pressed to shape under apredetermined pressure and then placed centrally in a larger mold cavitywith the uncolored ceramic material pressed around it. By shaping bothpieces at the same pressure, the problem of shrinkage cracks again canbe minimized.

LII

' l 2. Aball mill according to claim 1 wherein said colored A markingbrick 36 of FIG. 5 has a recess 38 in which a marking section or insert40 is located. The brick 36 can be either extruded in accordance withthe method discussed for the brick 24 or can be molded in accordancewith the method discussed for the brick 30. The important feature of thebrick 36 is that the sides of the insert 40 extending toward the face ofthe brick taper so that more of the colored section is exposed as moreof the brick wears. in this manner, the amount of wear can be determinedby the width of the exposed colored section. The thickness of thesection 40 may exceed that of the sections 28 and 34 but again will notnormally exceed approximately one-third the thickness of the overallbrick.

While the section 40 is shown in an elongated shape, it also can be madein the form of a cone or pyramid, if the brick is molded similarly tothe brick 30. The sides of the section 40, rather than tapering towardone another, in a direction toward the face of the brick, can taper inthe opposite direction so that the exposed portion narrows as wearincreases.

various rriodmations of the above described embodiments of the inventionwill be apparent to those skilled in the art, and

his to'be understood that such modifications can be made withoutdeparting from the scope of the invention, if they are within the spiritand the tenor of the accompanying claims.

lclaim: 1. A ball mill comprising wall means forming a generallycylindrical chamber, a ceramic liner for said chamber, and means forrotating said wall means, said ceramic liner for said chamber comprisinga plurality of bricks lining said chamber and located in contiguousrelationship, said plurality including a predetermined number of markingbricks disposed among said plurality in predetermined positions, each ofsaid marking bricks having a recess in the back thereof extendinginwardly toward the face, said recess being filled with a coloredmaterial which, when exposed, is readily distinguishable to the eye fromthe remainder of the brick, said colored material being substantially ofthe same size and shape as said recess.

material is a ceramic material.

3. A ball mill according to claim 1 characterized by said coloredmaterial having a thickness from one-eighth to onethirdthe oyer allthickness of themarking brick.

4. A ball mill according to claim 1 wherein said colored materialincludes a coloring agent present in an amount not exceeding about 2percent by weight. 7

s. A ball mill accordin g to claim 1 wherein each of said marking brickscomprises ceramic material constituting at least percent alumina, byweight.

6. A b all mill according to claim 4 wherein said coloring agentconsists of an oxide selected from the group consisting of cobalt,nickel iron, chromium, and manganese.

7. A ball mill according to claim 5 wherein said colored materialcomprises alumina and a colorant not exceeding about 2 percent of thecolored material, by weight.

1. A ball mill comprising wall means forming a generally cylindricalchamber, a ceramic liner for said chamber, and means for rotating saidwall means, said ceramic liner for said chamber comprising a pluralityof bricks lining said chamber and located in contiguous relationship,said plurality including a predetermined number of marking bricksdisposed among said plurality in predetermined positions, each of saidmarking bricks having a recess in the back thereof extending inwardlytoward the face, said recess being filled with a colored material which,when exposed, is readily distinguishable to the eye from the remainderof the brick, said colored material being substantially of the same sizeand shape as said recess.
 2. A ball mill according to claim 1 whereinsaid colored material is a ceramic material.
 3. A ball mill according toclaim 1 characterized by said colored material having a thickness fromone-eighth to one-third the overall thickness of the marking brick.
 4. Aball mill according to claim 1 wherein said colored material includes acoloring agent present in an amount not exceeding about 2 percent byweight.
 5. A ball mill according to claim 1 wherein each of said markingbricks comprises ceramic material constituting at least 85 percentalumina, by weight.
 6. A ball mill according to claim 4 wherein saidcoloring agent consists of an oxide selected from the group consistingof cobalt, nickel, iron, chromium, and manganese.
 7. A ball millaccording to claim 5 wherein said colored material comprises alumina anda colorant not exceeding about 2 percent of the colored material, byweight.